The present invention relates to a steering apparatus employed, for example, in industrial vehicles, more specifically to a steering apparatus provided with a toe-angle adjusting mechanism.
Generally, industrial vehicles, such as forklift trucks, are each provided with a steering apparatus for steering a pair of wheels in response to operation of a steering wheel. It is necessary to correctly set the direction of the wheels, or the relationship between the toe angle and the rotational position of the steering wheel, such that the vehicle travels along a straight line when the steering wheel is in the neutral position. However, discordance occurs in the relationship between the toe angle and the rotational position of the steering wheel due to errors in machining various parts of the steering apparatus and assembly errors, which may prevent the vehicles from running smoothly. Therefore, a step of correcting deviation of the toe angle is performed after wheels are attached to the rear axle.
Japanese Unexamined Patent Publication (KOKAI) No. Hei 10-76977 discloses a steering apparatus provided with a toe-angle adjusting mechanism. As shown in FIG. 10, the steering apparatus 71 is located in a rear axle 70 of a vehicle. A pair of steering knuckle arms 74 supporting a pair of rear wheels 76 are pivotally supported by kingpins 79 at the ends of the rear axle 70, respectively. Each rear wheel 76 can be steered together with the steering knuckle arm 74 about the axis of the kingpin 79.
The steering apparatus 71 includes a cylinder 73 having an operating rod 72. The operating rod 72 has connecting pieces extended toward the rear wheels 76, respectively. The pair of steering knuckle arms 74 are connected to the connecting pieces of the operating rod 72 through tie rods 75, respectively. Each tie rod 75 and each steering knuckle arm 74 are connected pivotally relative to each other by a substantially cylindrical connecting shaft 77. The connecting piece of the operating rod 72 and the tie rod 75 are connected pivotally relative to each other by an adjusting pin 78. Axial movement of the operating rod 72 is converted by the tie rod 75 into pivotal movement of the corresponding steering knuckle arm 74 about the kingpin 79.
As shown in FIG. 11, the adjusting pin 78 has a hexagonal head 78d, an upper supporting shaft portion 78b, an eccentric shaft portion 78a and a lower supporting shaft portion 78c. The axis of the eccentric shaft portion 78a (eccentric shaft axis X2) is offset by a predetermined distance, or the offset value T1, from the axis (main axis X1) of the upper and lower supporting shaft portions 78b and 78c and of the hexagonal head 78d. The adjusting pin 78 is fitted in an upper pin hole 72a and a lower pin hole 72b formed coaxially in the operating rod 72. The eccentric shaft 78a is abutted only against the inner surface of a collar 80, which is fitted in a pin hole 75a formed in the tie rod 75. The hexagonal head 78d is fitted in a hexagonal hole defined in a locking plate 81. The locking plate 81 is fixed to the operating rod 72 by a bolt 82. The plate 81 prevents rotation of the adjusting pin 78.
In adjusting the toe angle, the locking plate 81 is detached from the hexagonal head 78d, and the adjusting pin 78 is turned. The eccentric shaft axis X2 moves along an imaginary circle, the radius of which is the offset value T1, drawn around the main axis X1. The distance between the main axis X1 of the adjusting pin 78 and the axis of the connecting shaft 77 is changed depending on the position of the eccentric shaft axis X2, or the eccentric shaft 78a. The position of the knuckle arm 74 depends on this distance. The adjusting pin 78 is locked by fitting the locking plate 81 to the pin 78 after it is adjusted. This fixes the relationship between the wheel 76 and the rotational position of the steering wheel and adjusts the direction, or toe angle, of the rear wheel 76.
In the conventional steering apparatus 71, the locking plate 81 is abutted against a restricting face 72c formed on the operating rod 72 for immobilizing the locking plate 81. This requires a step of forming the restricting face 72c on the operating rod 72.
Variation in the accuracy of parts and errors in assembling them cause variation in the maximum steering angle of the rear wheel 76. If the maximum steering angle is greater than a designed value, the rear wheel 76 can interfere with the body of the vehicle. However, the steering apparatus 71 does not account for errors in the maximum angle of the rear wheel.
Meanwhile, to form the eccentric shaft 78a having a great offset value T1 on the adjusting pin 78 requires a relatively thick adjusting pin 78 and a great amount of machining, which leads to high material costs and much trouble and time.
A first objective of the present invention is to provide a mechanism for adjusting toe angle of wheels and a steering apparatus that facilitate machining and assembly of an operating rod and connecting pins. A second objective of the present invention is to provide a toe angle adjusting mechanism for a vehicle and a steering apparatus that can accurately adjust the toe angle of a wheel.
To achieve the above objective, the present invention provides a toe-angle adjusting mechanism for adjusting a toe angle of a wheel. The mechanism includes a steering knuckle arm pivotally supporting the wheel, an operating rod, which reciprocates in response to operation of a steering wheel, a tie rod connecting the operating rod with the steering knuckle arm to convert reciprocating movement of the operating rod into a pivotal movement of the steering knuckle arm, an adjusting pin pivotally connecting the operating rod with the tie rod, a connecting pin pivotally connecting the steering knuckle arm with the tie rod, and a locking element fitted against the pins. The adjusting pin includes an eccentric section and an engagement section. An outer surface of the eccentric section contacts either the operating rod or the tie rod. The distance between the operating rod and the steering knuckle arm changes depending on the rotational position of the adjusting pin. The locking element engages the engagement section and the connecting pin to prevent rotation of the adjusting pin.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.